Method and device for operating a hybrid vehicle comprising an electric energy store, and electric motor and an internal combustion engine

ABSTRACT

A method and a device operate a hybrid vehicle having an electric energy store, an electric propulsion system and an internal combustion engine. A special operating strategy that can be initiated for the internal combustion engine allows the state of charge of the energy store to be increased when predefined acoustic conditions are met. The special operating strategy has a performance-enhancing effect by raising the load point until acoustic limits are reached which are ascertained in real time, can be predefined in a variable manner and are defined in accordance with ascertained potentials for masking specific acoustic events. The disclosed method and device for carrying out the method raise the acoustic limits for controlling the load point of the internal combustion engine at least to the level that is currently admissible as a result of at least one acoustically relevant event being masked.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/EP2017/058930, filed Apr. 13, 2017, which claims priority under 35U.S.C. § 119 from German Patent Application No. 10 2016 207 037.1, filedApr. 26, 2016, the entire disclosures of which are herein expresslyincorporated by reference.

This application contains subject matter related to U.S. applicationSer. No. 16/170,889, entitled “Method and Device for Operating a HybridVehicle Comprising an Electric Energy Store, an Electric Motor and anInternal Combustion Engine” filed on even date herewith.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method and an apparatus for operating ahybrid vehicle having an electric energy store, an electric motor as afirst drive motor, and an internal combustion engine as a second drivemotor.

A multiplicity of operating strategies of hybrid vehicles are alreadyknown that place their focus in particular on efficient driving.

The invention is based on the object of achieving a best possible stateof charge for the electric energy store given the best possible comforteven while traveling.

The invention fundamentally relates to a method and an apparatus foroperating a hybrid vehicle having an electric energy store (e.g.high-voltage battery), an electric drive and an internal combustionengine, wherein a special operating strategy for the internal combustionengine can be triggered that can achieve an increase in the state ofcharge of the energy store if prescribed acoustic conditions are met.The special operating strategy has a power-increasing effect by virtueof a raising of the load point to the point at which respectivecurrently ascertained, preferably variably prescribable, acoustic limitsare reached that are defined on the basis of ascertained maskingpotentials of particular acoustic events. In other words, a method andan apparatus for performing the method are proposed, which method raisesthe acoustic limits for controlling the load point of the internalcombustion engine at least to the level that is currently admissible ineach case on account of the masking of at least one acousticallyrelevant event.

To this end, the masking potentials of particular acoustically relevantevents are ascertained and, on the occurrence of multiple events havingdifferent masking potentials, are preferably used in coordinated fashionto define the respective acoustic limit currently needing to beprescribed.

The method according to the invention is performed by virtue ofapplicable programming of at least one electronic control unit intendedfor that purpose.

By way of example, in an implementation phase of the apparatus accordingto the invention for performing the method according to the invention,the individual masking potential is ascertained empirically, preferablyas an (individual) sound pressure spectrum, for each definedacoustically relevant event and is stored in the control unit. After ahybrid vehicle equipped with the invention is started up, a check isperformed to determine what acoustically relevant events are currentlyoccurring in each case. To coordinate the respective masking potentialscurrently available at the same time, the maximum of all maskingpotentials is preferably ascertained, in particular in the form of amaximum sound pressure spectrum. By way of example, the overall soundpressure spectrum thus formed is in particular compared with aload-dependent sound pressure spectrum of the internal combustionengine, which is considered as a sound source in this case, that islikewise kept in the control unit. That load point whose sound pressurespectrum is beneath the coordinated overall sound pressure spectrum ineach case, or is sufficiently masked thereby, is then chosen for theinternal combustion engine. The overall sound pressure spectrum is aparticularly advantageous exemplary embodiment of an acoustic limitvariably prescribable according to the invention. An acoustic limitcould also be directly prescribed as a motor torque. This variable isless suitable than the consideration of sound pressure spectra, however,on the basis of the frequency dependency of the motor acoustics and themasking.

A raising of the load point can be prescribed by an absolute load valueas a function of the respective occurring acoustically relevant maskingevents or else as the difference from a basic load value, which maylikewise be prescribed by a basic sound spectrum. A basic sound spectrumof this kind may also be ascertained empirically and stored in thecontrol unit, for example. By way of example, the basic sound spectrummay be an audible motor sound usually accepted as a maximum if noadditional masking events compared with a basic state (e.g.: on thebasis of speed-dependent wind noise or road noise, which is always atleast present, on a flat or smooth road) are occurring. The basic soundspectrum is subsequently also referred to as the basic state or basicacoustic threshold. The basic acoustic threshold is normally dependenton the running state, such as e.g. on the driver's desired drive torqueand on the speed.

Preferably, the following possible acoustically relevant events withtheir characteristic masking potentials are taken into consideration ontheir own or in any desired combination with one another:

-   1) Events as a result of vehicle-internal sources of influence, in    particular whose characteristic spectra are known and/or whose    occurrences are controlled by vehicle-internal systems, such as fans    of the air conditioning system, open windows or an open sliding    roof, preferably also on the basis of seat occupancy and/or vehicle    speed. In this case, wideband masking potentials, in particular, are    taken into consideration. By way of example, a distinction can also    be made between a standstill and a journey in this case.-   2) Events as a result of vehicle-external sources of influence, in    particular whose characteristic spectra are known and/or whose    occurrences are capturable by sensors, such as rain, road surface or    travel through a tunnel. In this case too, preferably wideband    masking effects are preferred.-   3) Events as a result of sources of influence caused by the user, in    particular as a result of the operation of audio installations, in    particular whose spectra are evaluable before or during    reproduction, such as audio installations whose data are stored on    hard disk, or digital radios with delayed computation or signal    propagation times.-   4) Events as a result of unknown sources of influence, in particular    whose spectra are unknown beforehand or that need to be captured via    at least one microphone, wherein in this case only a reduced masking    potential can be assumed on the basis of the expected high signal    dynamics, which may be higher than the adjustable dynamics of the    sound source (motor).

Still further events may be defined. Acoustically relevant events can beunderstood to mean both airborne sound emissions and vibrations.

Further Details re 1):

A first preferred exemplary embodiment assumes a comparatively highmasking potential with the fan of the heating and air conditioningsystem as control system switched on. Preferably, an increasing raisingof the load point in the sense of an increasing motor torque of theinternal combustion engine is therefore fundamentally performed forcharging as the fan level increases (at at least one level through tocontinuous adjustment). In this case, the raising of the load point canbe performed when the vehicle is at a standstill by virtue of anabsolute value, independently of the basic state or of a basic acousticthreshold. While traveling, the raising of the load point can beperformed on the basis of the fan level as an offset relative to thebasic state or to a basic acoustic threshold.

A second preferred exemplary embodiment assumes a comparatively highmasking potential with a window and/or sliding roof open, wherein inthis case the control systems for opening and closing the windows andthe sliding roof know the current aperture width thereof. These can thenlikewise have empirically ascertained applicable masking potentialsassigned to them. In this case, the masking potential can also bedetermined on the basis of the position of an open window in relation tothe position of an occupied seat. With regard to the sliding roof, it ispossible, by way of example, for two or more aperture dimensions to beassigned to two or more different masking potentials.

The masking potentials and the number of levels of the maskingpotentials, in this case depending on the fan level or on the degrees ofopening, for example, can be ascertained empirically and stored in theform of torque or spectra characteristic curve families.

Further Details re 2):

A first preferred exemplary embodiment assumes a comparatively highmasking potential in the event of rain. Detection of this event ispossible e.g. by means of a rain sensor, use of the windshield wiperand/or by means of radar sensors for distance measurement. Preferably,to distinguish between rain and snow, the outside temperature is alsoevaluated, for example.

A second preferred exemplary embodiment assumes a comparatively highmasking potential in the case of a rough and/or uneven road surface.Detection of this event is possible e.g. on the basis of signals fromthe chassis control systems.

A third preferred exemplary embodiment assumes a comparatively highmasking potential in the event of travel through a tunnel. Detection ofthis event is possible e.g. by means of cameras for distance control orfor lane change assistance and/or by means of road data from anavigation system and/or brightness sensors for low beam control.

Fundamentally, it is assumed that influences from outside alsofundamentally result in particular masking effects that can be used forincreasing (for a limited time) the raising of the load point. Theoccurrence and level of the masking potential are captured for differentaspects by means of respective suitable vehicle sensors, where possible.Subsequently, as with any defined detected masking potential, it isassigned to maximum admissible acoustic thresholds for possible loadpoint raises.

Further Details re 3):

Masking is provided on the basis of the output spectrum and the volumeof the audio installation, for example. To determine the maskingpotential of the audio installation, analysis or matching of this outputspectrum with the drive acoustics on which the basic acoustic limits arefundamentally based is required. In this case, the drive acoustics canbe introduced e.g. by spectra ascertained and stored in advance. Thesespectra are dependent in particular on motor speed, load, speed and/orgear.

On the basis of computation complexity and signal propagation times,there is provision for a short delay in the audio reproduction. Foraudio data (such as e.g. data stored on the hard disk) or audio sourceswith an inherent computation and signal propagation time (such as e.g.digital sources such as DAB, DVB-T, satellite radio or the like) thatare already present in the vehicle, the masking potential can alsoalready be ascertained offline or appropriately in advance. In thiscase, the source can be evaluated before the output, but also inparallel with the output in advance. The necessary degree of advance forthe computation of the masking potential can also be provided morequickly than in real time by virtue of the design of a buffer for outputby means of computation of the audio output. Provision can be made forall or some of the computations needed for output during the D/Aconversion of the digital sources to be used for the spectral analysisneeded for ascertaining the masking potential, in order to usesynergies.

In the event of the masking potential abruptly becoming much lower basedon the output spectrum of the audio installation, the proportion of loadpoint raising also first needs to be reduced abruptly on the basis ofthis masking potential. Additionally, it may also be desirable to lowerthe raising of the load point even below the static supply of data (thatis to say beneath the basic acoustic limit) so that the quiet audioexperience is tarnished all the less by the acoustics of the internalcombustion engine.

This process involves multiple controllers in the vehicle:

a) controller(s) for the audio installation,

b) controller(s) for the drive.

To ascertain the masking potential, the following steps are necessary:

1. ascertaining the spectrum of the output for the audio installation.

2. establishing the operating point or the motor speed

3. ascertaining the maskable motor load on the basis of the spectrumfrom step 1 and from stored spectra of the motor acoustics.

4. implementing the ascertained masking potential by possibly increasingthe raising of the load point.

By way of example, step 1 can be performed on controller a) and steps 2and 4 can be performed on controller b).

For step 3, there are the following options requiring differentcommunication processes between controllers a) and b). The controller b)for the stored spectra of the motor acoustics can also vary:

-   i. step 3 takes place on controller b).

In this case, the spectra ascertained in step 1 in controller a) need tobe routed to controller b).

The spectra of the motor acoustics are on controller b).

-   ii. step 3 takes place on controller a).

The operating point needs to be sent from controller a) to controllerb), and the ascertained masking potential in turn from a) to b).

The spectra of the motor acoustics are on controller a).

-   iii. As ii., but not only a masking potential is sent from a) to b),    but rather a family of characteristic curves for the potential. The    aforementioned degree of advance means that the future operating    point is known only approximately. The potential is therefore    ascertained not only for a particular operating point, but rather    for the current operating point and its direct “surroundings” or    else for further operating points having a high probability of    occurrence. As such, a family of characteristic curves for potential    is obtained for multiple operating points, instead of a “potential    value” for one operating point.    Further Details re 4):

Acoustic masking with a dynamic spectrum can also be factored into theformation of the acoustic limits in a manner according to the invention.This requires the significant effects to be identified and communicatedto the motor control/operating strategy in this case too. On the basisof the masking, acoustic limits can be raised again.

Masking can have every possible cause in this case, which does not haveto be known more specifically, however. In the interior, the airbornesound spectrum can thus be measured by one or more microphones. Todetermine the masking potential, analysis or matching of this measuredspectrum with the drive acoustics (basic acoustic limits) is necessaryin this case too.

As the dynamics of the microphone signal may be very high, it isnecessary to be able to react with the raising of the load pointaccordingly quickly. This reaction speed is related inter alia to thedynamics of the internal combustion engine, which are determined interalia by the dynamics of the filling and the dynamics of the ignitionangle. In this case, the dynamics of the ignition angle are much higherthan those of the filling. In the event of an increase in torque,adequate filling is a prerequisite for high dynamics as a result of achange in the ignition angle, however. Controlling the motor torque bymeans of the filling is better for consumption, but if the dynamicsthereof are not sufficient for the required reaction time, it isnecessary to react by means of the ignition angle.

It is possibly necessary, owing to the high dynamics of the microphonesignal and the shortest possible interval of time between microphonesignal and enabling of the raising of the load point, to keep theadditional raising of the load point that is enabled from thisfunctionality rather small so that it can also quickly be reduced again.If the interval of time between microphone signal and enabling of theraising of the load point becomes too long, it may be that the raisingof the load point is still increased even though there are already nofurther masking sounds in the interior of the vehicle. The considerationof the events according to item 4) is thus probably possible only to alimited extent and very briefly.

Preferably, it is possible to check whether a raising of the load pointon the basis of an identified masking potential is intended to beprevented or reduced by an acoustically opposite event.

As a development of the invention or as an independent concept, theoccurrence of an acoustically opposite event can result in a lowering ofthe load point, even to the point of the internal combustion enginebeing switched off, either on the basis of or independently of anavailable masking potential. An acoustically opposite event may be asituation in which, by way of example, there is no or only littlemasking and/or in which there is an acoustic exceptional situation withcomparatively low probability of occurrence in which particularly fewinterference signals are desirable, e.g. in the case of an incomingtelephone call. An acoustically opposite event could also be an openwindow at a standstill as a result of which the sounds and/or vibrationsof the internal combustion engine are perceived to a greater extent thanusual.

As a result of the invention, the defined events having the applicablemasking potentials are preferably used in coordinated fashion for theraising of the acoustic limits for raising the load point or varying theload point.

The invention is based on the following considerations:

In hybrid vehicles, variation of the load point of the internalcombustion engine, in particular raising of the load point, is limitedby acoustic limits in order to avoid acoustic anomalies. According tothe prior art, these acoustic limits, subsequently also called basicacoustic limits, are empirically regulated in particular on the basis ofstatic vehicle properties and operating points of the drive (e.g. on thebasis of vehicle speed, driver's desired torque, motor torque, motorspeed and gear).

Fundamentally, the acoustic limits can be raised for a particularly highpower requirement that exists, for example, in the event of increasedvehicle electric system load and/or low state of charge. However, thispossibly results in undesirable sensitivity to noise for the driver.

As a result of a wide variety of sources and changes to the transmissionpaths (e.g. as a result of vehicle-external influences such as rain,road surface and travel through a tunnel or as a result ofvehicle-internal influences such as fans of the air conditioning system,open windows, open sliding roof, folded rear seat and seat occupancy oras a result of influences caused by the user such as telephone calls,conversations and music sources via vehicle-internal or independentaudio installations), there are airborne sound emissions in the vehicleinterior whose masking potential can be ascertained in each case usingdifferent methods (such as, for example, by using at least one interiormicrophone, by analyzing a played-back audio source in the vehicle orindirectly by virtue of derivation from signals from the vehiclesensors, such as the rain sensor, the height sensors or the navigationdata, for example).

The masking allows the acoustic limits to be raised without losses ofcomfort.

Simultaneous use of multiple possible masking potentials (individual oroverlaid masking potentials) involves a coordination method forascertaining resultant acoustic limits being provided according to theinvention. This allows an improvement in the overall acoustic behaviorto be achieved.

This first of all involves the individual masking potentials fordifferent sources (or acoustic events) having particular properties(subsequently also called aspects, with in particular characteristicacoustic spectra being included) being ascertained (see also theaforementioned examples 1) to 4) for possible acoustically relevantevents or sources).

Subsequently, the ascertained individual masking potentials arecoordinated as follows, for example:

-   1. First, the masking potential is ascertained per aspect or per    event having an applicable acoustic spectrum.-   2. Subsequently, the maximum is ascertained from all (possibly    simultaneously available) masking potentials, the acoustic limits    dependent on the static vehicle properties and operating points of    vehicle and drive preferably also being able to be taken into    consideration in the form of the aforementioned basic acoustic    limits (basic state).-   3. Lastly, the check can preferably also be performed to determine    whether a raising of the load point on the basis of an identified    masking potential is prevented or reduced by an acoustically    opposite event. By way of example, a possible raising of the load    point on the basis of an open window could be ascertained that could    be perceived as acoustically more disruptive again at a standstill    or during a telephone call than while traveling, however.-   4. The “new” acoustic limit respectively ascertained in this manner    for a current operating state is then enabled and forms the upper    limit for the raising of the load point if, should the situation    arise, there is no other check result available in item 3. that    leads to a lowering of the upper limit (even below the basic    acoustic limits).

For steps 1. and 2., there are the following options, for example, whichare applicable alternatively or together:

-   I. The potentials are each ascertained for the current operating    point as a torque (in newton meters [Nm]) and subsequently combined.-   II. The potentials are ascertained and combined as an (airborne)    sound spectrum (in decibels [dB]) for the present. This preferred    alternative is explained in even more detail later on in an    exemplary embodiment (with reference to the drawing).

In detail, option I. may be configured as follows:

First, the respective acoustic limits in newton meters [Nm] areascertained for the respective aspects, either directly as absolutevalues or first relative to the currently applicable basic acousticlimit. One example for the case as a relative value: on the basis of therunning highest fan level of the air conditioning system, the internalcombustion engine can provide 5 [Nm] more torque for charging the energystore (e.g. high-voltage battery). Subsequently, the relative values areconverted into absolute values by adding them to the current basicacoustic limit. The maximum value is then computed from the variousacoustic limits and is then the “new” acoustic limit.

In detail, option II. may be configured as follows:

First, (airborne) sound spectra are ascertained for respective aspects.These are measured directly (e.g. in the case of masking ascertainmentby means of interior microphones), ascertained directly (e.g. in thecase of masking ascertainment by means of the output signal from theaudio installation) or ascertained indirectly (using state detection bymeans of sensors or control systems and stored spectra, e.g. in the caseof travel through a tunnel, an open window at significant speeds or highinterior fan levels). Subsequently, the maximum is computed from thesevarious sound spectra, for example per one-third octave band, as theoverall sound spectrum.

On the basis of this one-third octave spectrum, the maximum order levelfor the relevant internal combustion engine orders for the current motorspeed or corresponding frequencies is then determined. This can beeffected, for example, on the basis of an interval, possibly dependenton frequency, between the cumulative level of the spectrum and the orderlevel or else using tonality methods that can compute the level at whichtonal components can be masked by wideband spectra.

From this/these maximum order level(s), a maximum internal combustionengine load in newton meters [Nm] is subsequently derived on the basisof stored data from airborne sound order levels in the interior fordifferent internal combustion engine loads.

The “new upper limit” (new acoustic limit) according to option II. isthen determined as the maximum of this ascertained internal combustionengine load and possibly of the “static” basic acoustic limit valid atthe respective operating point.

If a mixture of options I. and II. is used, the acoustic limits innewton meters that are ascertained according to option I. can be used inthe method according to option II. at this juncture.

Regardless of whether the upper limits or the “new” acoustic limits areascertained according to option I. or option II., it is preferably alsoascertained, in parallel with the ascertainment of the “new upperlimits”, whether the raising of the load point in the current operatingstate of the vehicle is intended to be limited for a specific reason(e.g. acoustically opposite event):

The reasons for limiting the raising of the load point despite theoccurrence of masking events or even for a reduction in the acousticlimit are normally states that strongly influence the transmission path,but have a low probability of occurrence and accordingly are also nottaken into consideration in the “static” supply of data for the basicacoustic limit, because this would lead to heavy permanent limitationsfor the raising of the load point. Examples that may be cited here areopen windows at a standstill on account of a direct repercussion of theexhaust system mouth sound.

In addition, there is provision for the raising of the load point to belimited despite the occurrence of masking events or even for theacoustic limits to be reduced on the basis of temporary, quasi-staticand/or dynamically increased acoustic demands. An example of aquasi-static state is an incoming/ongoing telephone call. Acorresponding dynamic event may be e.g. a passage with a greatly reducedvolume in the music played back by the audio installation.

In this regard, enable requests and applicable reduced upper limits canbe ascertained in separate software functions. Furthermore, in this casetoo, the overall energy state of the vehicle can be taken intoconsideration and, for example, a reduction in the raising of the loadpoint can be prevented in the event of a very low state of charge in thehigh voltage store.

To conclude the coordination, the final acoustic limit as the minimum ofthe “new upper limit” and the lowest enabled reduced upper limit isestablished and enabled.

In parallel with the masking of the airborne sound in the interior, itis also possible to use masking potentials for vibrations. For example,vibrations at the seat, caused by stimulation from the internalcombustion engine, can impair comfort and can be masked by vibrationscaused by a poor road surface. These masking potentials can then alsopreferably be coordinated as acceleration spectra. The sequence forascertaining the upper limits on the basis of vibrations takes place inan analogous manner to the airborne sound. The contributions arelikewise combined either “in newton meters” (according to option I.) or“by means of acceleration spectra” (option II.). The upper limits on thebasis of the airborne sound with the upper limits on the basis ofvibrations are preferably combined “in newton meters”.

When the various masking potentials are used, the occurrence thereof canbe taken as a basis for improving the hybrid properties (e.g.: electricdriving components, air conditioning performance) without limitingcomfort. An acoustically rather uncomfortable raising of the acousticlimits only in the event of significantly increased need and/or only inthe event of a very low state of charge in the high-voltage store willoccur less frequently. The invention affords the advantage of optimumcoordination of the individual presets from the static vehicleproperties and operating points (basis) and from the individualfunctions for ascertaining the respective current individual or overallmasking potential. The coordination contributes to further diffusing theconflict of aims between hybrid properties and comfort.

Until a target state of charge is reached, it is therefore possible formore intense charging to be performed, even without more highlyperceptible noise, than during regular operation and/or (alternativelyor additionally in a second step for an even greater power increase) forefficient operating points of the internal combustion engine to be usedthat could not be used otherwise on the basis of acoustic limits. Theemission increase briefly caused as a result is compensated for again bythe stored electric power for driving the emission-free electric motor.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of one ormore preferred embodiments when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of an overview of the essentialcomponents of the invention.

FIG. 2 is an example of a first individual masking potential.

FIG. 3 is an example of a second individual masking potential.

FIG. 4 is an example of a third individual masking potential.

FIG. 5 is an example of a fourth individual masking potential.

FIG. 6 is a graph for the inventive ascertainment of a “new”overall-masking-dependent acoustic limit in the case of overlaid maskingpotentials according to the aforementioned option II.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an input/output display 1 at least for the output ofinformation pertaining to the specific method of operation according tothe invention. The display 1 is actuated via an electronic control unit7. The current state of charge SOC of an electric energy store 2, inthis case a high-voltage battery, is captured and forwarded to thedisplay 1.

A further input signal for the control unit 7 will be the status of anair conditioning fan 3, for example, in this case as an example of apossible acoustically relevant event by a vehicle-internal source ofinfluence whose characteristic spectrum is known and whose occurrence iscontrolled by a vehicle-internal system, in this case the airconditioning system. The masking potential of the air conditioning fan 3is indicated by Ml.

A further input signal for the control unit 7 will be the status of asensor arrangement 4 for detecting travel through a tunnel, for example,in this case as an example of a possible acoustically relevant event bya vehicle-external source of influence whose characteristic spectrum isknown and whose occurrence is capturable by sensors, in this case by acamera in conjunction with a navigation system, for example. The maskingpotential of detected travel through a tunnel is indicated by M2.

A further input signal for the control unit 7 will be the signal from anaudio installation 5, for example, in this case as an example of apossible acoustically relevant event by a user-caused source ofinfluence whose characteristic spectrum is evaluable before or duringreproduction. The masking potential of the current output from an audioinstallation 5 is indicated by M3.

A further input signal for the control unit 7 will be the input signalfrom a microphone 6, for example, in this case as an example of apossible acoustically relevant event by an unknown source of influencewhose characteristic spectrum is unknown beforehand and is ascertainableonly highly dynamically. The masking potential of the airborne soundspectrum currently captured by means of the microphone 6 (for example aconversation by vehicle occupants) is indicated by M4.

The masking potentials M1 to M4 are ascertained in a functional module 8of the controller 7 and if need be coordinated.

The individual masking potential M1 of the air conditioning fan 3 isdepicted by way of example in FIG. 2.

The individual masking potential M2 of detected travel through a tunnelis depicted by way of example in FIG. 3.

The individual masking potential M3 of the current output for an audioinstallation 5 is depicted by way of example in FIG. 4.

The individual masking potential M4 of the airborne sound spectrumcurrently captured by means of the microphone 6 is depicted by way ofexample in FIG. 5.

The masking potentials are depicted in decibels [dB] in this case andrelative to a basic acoustic threshold BA in this case.

FIG. 6 uses an example graph to show the mode of action of thecoordination method according to the invention performable by virtue ofappropriate programming of the functional module 8. In this case, a(one-third octave) sound pressure spectrum of the audio installation 5,or the masking potential M3, and a (one-third octave) sound pressurespectrum as a result of traveling through a tunnel, or the maskingpotential M2, are depicted, which together form a new (one-third octave)spectrum or a cumulative masking potential MAX (M2, M3) or an overallsound pressure spectrum (denoted by the bold line).

Subsequently, it is ascertained how high the order level of the internalcombustion orders is that can be masked by this overall sound spectrum.Stored data are then used to convert this order level into a motortorque in newton meters [Nm]. At the end of this partial process, thematching with the basic acoustic limit BA then takes place, in [Nm], ifneed be, said basic acoustic limit being dependent on the static vehicleproperties and operating points of vehicle and drive.

The basic acoustic limit BA can be prescribed preferably when none ofthe other masking potentials M1 to M4 are available.

In a particular configuration of the invention, when there is a specificreason, it is also possible for a “lower acoustic limit”, which may evenbe beneath the basic acoustic limit, to be prescribed on the basis of orindependently of the occurrence of a masking acoustically relevantevent. This prevention or reduction of the raising of the load point orthis lowering of the load point—even below the basic acoustic limit orindependently of a basic acoustic limit—can be regarded not only as adevelopment of the invention but also as an independent concept. By wayof example, a lowering of the load point can be used as an extended“mute” function for a telephone call. In this case, depending on thestate of charge, it would also be possible to change over to fullelectric driving.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A method for operating a hybrid vehicle having anelectric energy store, an electric drive and an internal combustionengine, the method comprising the acts of: triggering a raising of aload point for the internal combustion engine to increase a state ofcharge of the energy store on the basis of prescribed acoustic limits,wherein the prescribed acoustic limits are determined on the basis ofmasking potential of at least one currently occurring acousticallyrelevant event defined therefor, wherein masking potentials of thecurrently occurring acoustically relevant events on the occurrence ofmultiple events having different masking potentials for defining therespective acoustic limit currently needing to be prescribed arecoordinated in the form of a determination of an overall maskingpotential, and wherein at least one of: the individual maskingpotentials and the overall masking potential, is prescribed in the formof sound pressure spectra.
 2. The method as claimed in claim 1, whereindetermining the overall masking potential involves a maximum of allsimultaneously available masking potentials being ascertained.
 3. Themethod as claimed in claim 1, wherein a check is performed to determinewhether an acoustically opposite event either performs a lowering of theload point, even to the point at which the internal combustion engine isswitched off, on the basis of or independently of an available maskingpotential or prevents or reduces a raising of the load point despite amasking potential being available.
 4. The method as claimed in claim 1,wherein possible acoustically relevant events are defined byvehicle-internal sources of influence whose characteristic spectra areknown by virtue of empirical ascertainment and whose occurrences arecontrolled by vehicle-internal systems.
 5. The method as claimed inclaim 4, wherein possible acoustically relevant events are defined byvehicle-external sources of influence whose characteristic spectra areknown by virtue of empirical ascertainment and whose occurrences arecapturable by sensors.
 6. The method as claimed in claim 1, whereinpossible acoustically relevant events are defined by vehicle-externalsources of influence whose characteristic spectra are known by virtue ofempirical ascertainment and whose occurrences are capturable by sensors.7. The method as claimed in claim 5, wherein the possible acousticallyrelevant events defined are output signals from audio installationswhose spectra are evaluable before or during reproduction.
 8. The methodas claimed in claim 1, wherein possible acoustically relevant eventsdefined are output signals from audio installations whose spectra areevaluable before or during reproduction.
 9. The method as claimed inclaim 5, wherein possible acoustically relevant events are defined byunknown sources of influence whose spectra are unknown beforehand andthat are captured via at least one microphone, wherein only a briefmasking potential is assumed in this case on the basis of the expectedhigh signal dynamics.
 10. The method as claimed in claim 1, wherein thepossible acoustically relevant events are defined by unknown sources ofinfluence whose spectra are unknown beforehand and that are captured viaat least one microphone, wherein only a brief masking potential isassumed in this case on the basis of the expected high signal dynamics.11. A computer program product comprising a non-transitory computerreadable medium having stored thereon program code segments that, whenexecuted by a processor of an electronic control unit, carry out theacts of: triggering a raising of a load point for an internal combustionengine to increase a state of charge of an energy store on the basis ofprescribed acoustic limits, wherein the prescribed acoustic limits aredetermined on the basis of masking potential of at least one currentlyoccurring acoustically relevant event defined therefor, wherein maskingpotentials of the currently occurring acoustically relevant events onthe occurrence of multiple events having different masking potentialsfor defining the respective acoustic limit currently needing to beprescribed are coordinated in the form of a determination of an overallmasking potential, and wherein the individual masking potentials and/orthe overall masking potential are prescribed in the form of soundpressure spectra.
 12. A hybrid vehicle, comprising: an electroniccontrol unit; and a computer readable medium having stored thereonprogram code segments that, when executed by the processor of anelectronic control unit, carry out the acts of: triggering a raising ofa load point for an internal combustion engine to increase a state ofcharge of an energy store on the basis of prescribed acoustic limits,wherein the prescribed acoustic limits are determined on the basis ofmasking potential of at least one currently occurring acousticallyrelevant event defined therefor, wherein masking potentials of thecurrently occurring acoustically relevant events on the occurrence ofmultiple events having different masking potentials for defining therespective acoustic limit currently needing to be prescribed arecoordinated in the form of a determination of an overall maskingpotential, and wherein the individual masking potentials and/or theoverall masking potential are prescribed in the form of sound pressurespectra.